Lesson focus: gas pressureThe push of gas particles hitting the walls of their container. is force per area caused by particle collisionWhen particles bump into each other or into a surface. with surfaces.
Explain temperature and volume effects under clearly fixed conditions.
Build on earlier learning
DiffusionApply random particle motion to collisions with container walls.
Practical
Gas pressure in a sealed syringe
- Seal a syringe with some air inside.
- Push the plunger in and feel the resistance increase.
- Use the model on this page to see how volume and temperature change the pressure.
Record: How pressure changes when the volume decreases and when the temperature rises, with particle explanations.
Gas pressure in a sealed syringe
Push the plunger in or warm the gas. The same particles hit the walls more often, so the pressure rises.
Controls
You will be successful when you can…
- Define pressure as force per area.
- Explain pressure from collisions.
- Explain heating at fixed volume.
- Compare rigid and flexible containers.
Words that carry the science
- gas pressure
- Force per unit area exerted by gas on a surface.
- collision
- Interaction when a particle strikes a surface or another particle.
- rigid container
- Container whose volume remains effectively fixed.
- sealed container
- Container that does not allow matter to enter or leave.
- constant temperature
- Condition in which average particle kinetic energy is controlled.
State what is fixed before predicting pressure
01Collisions create force
Particles repeatedly change momentum when they strike walls. The combined impacts produce a force; pressure = force ÷ area.
02Heating at fixed volume
For a fixed amount in a rigid sealed containerA closed container that nothing can get into or out of., higher temperature increases average speed, collisionWhen particles bump into each other or into a surface. frequency and momentum change, so pressure rises. In simple steps: gas particles hit the walls of the container, and each hit pushes on the wall. That push is the gas pressureThe push of gas particles hitting the walls of their container.. When the gas is heated, the particles move faster, so they hit the walls more often and harder. So the pressure goes up.
03Compression at fixed temperature
Reducing volume shortens travel between walls, increasing collision frequency. A flexible balloon may expand on heating, so volume is not fixed.
Audit the conditions
A sealed metal can is heated from 20 °C to 60 °C.
- Sealed means amount of gas is fixed.
- Metal can is approximately rigid, so volume is fixed.
- Heating raises average particle speed.
- More frequent/harder collisions raise wall force and pressure.
How to make the reasoning visible: Name fixed amount and fixed volume before concluding pressure rises.
Pressure predictions
Each row states which variables are controlled.
| Change | Fixed | Prediction | Reason |
|---|---|---|---|
| Heat rigid can | Amount, volume | Pressure rises | Faster/harder collisions |
| Compress syringe slowly | Amount, temperature | Pressure rises | More frequent collisions |
| Heat flexible balloon | Amount | Volume increases | Wall can move |
| Release valve | Temperature, volume initially | Pressure falls | Particles leave |
Why is “sealed” insufficient to guarantee a large pressure rise?
Why must amount of gas be stated?
Use the table. Why does pushing in a sealed syringe increase the pressure?
Check your understanding
Answer from memory, then check against the suggested answer.
What is gas pressure?
What is collision?
What is rigid container?
What causes gas pressure?
What happens to gas pressure in a sealed can when it is heated?
Why are aerosol cans labelled “do not heat”?
Why can a balloon become larger in warmth?
Why do aerosol cans warn “Do not heat”?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A gas is sealed in a strong container that cannot change size. Answer the parts to explain why heating the gas makes its pressure go up.
What happens to the speed of the gas particles when they are heated?
(1)What happens to the number of times the particles hit the walls each second?
(1)How hard do the particles hit the walls?
(1)So what happens to the pressure?
(1)Total for this question: 4 marks
Command word: Follow the chain: faster → more hits → harder hits → more pressure.